In some fuel cells such as a polymer electrolyte fuel cell, which generates power using energy produced by a chemical reaction between hydrogen and oxygen, it is necessary to humidify the fuel cell to permit the fuel cell to function. The fuel cell itself generates heat when it generates power, so a cooling system is required which cools the fuel cell by cooling water or the like.
In a fuel cell system comprising a fuel cell using water, if the system is left below freezing point when it has stopped, the water or cooling water in the cell freezes and can cause damage or interfere with restart of the fuel cell system. JP7-169475A published in 1995 and JP11-214025A published by the Japanese Patent Office proposes a method for preventing freezing of the fuel cell.